docs: def _pdist(p):
          """ Return PL or ECPL instance based on parameters p """
          index, ref, ampl, cutoff, beta = p[:5]
          if cutoff == 0.0:
              pdist = models.PowerLaw(
                  ampl * 1e30 * u.Unit("1/eV"), ref * u.TeV, index
              )
          else:
              pdist = models.ExponentialCutoffPowerLaw(
                  ampl * 1e30 * u.Unit("1/eV"),
                  ref * u.TeV,
                  index,
                  cutoff * u.TeV,
                  beta=beta,
              )
          return pdist